Which preposition to use with nicaea

on Occurrences 2%

At a conference held at Nicaea on the Maliac gulf the king appeared in person, and endeavoured to come to an understanding with Flamininus.

as Occurrences 1%

" Kilidge-Arslan, being beaten, withdrew to collect fresh troops, and, after six weeks' siege, the crusaders believed themselves on the point of entering Nicaea as masters, when, on the 26th of June, they saw floating on the ramparts the standard of the Emperor Alexis.

Which preposition to use with  nicaea